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Full text of "Text Book Of Mechanical Engineering"

840

Appendix II.

:t

1°, tt

Now stress variation must be put in terms of maximum stress, and
this again in terms of/%, the new breaking stress, thus :

highest stress - lowest stress

highest stress
Case I. Ultimate static stress = 30 tons

S - 6~5/ - 1/'

D   —  —7-/2   -      /

X/2

(2*1/2x30)

27*25 tons square inch.
30 tons
• _ 5 *

2  —   6/2

.'./2 =

Solving the quadratic, /2 =
Case II. Ultimate static stress =

S-6^L

•'• A = A/2 + N/302 ~ (2 X |/2 X 30s)

Solving as before, j^ = 257 tons square inch.

The value of x in this formula may be 1-5 for iron and 2 for
steel in general, but varies considerably, the deductions from
Wohler's and Bauschinger's experiments being:

Iron

Bar Iron (Wohler)
Bar Iron (Bauschinger)
Bar Iron (ditto)
Plate Iron (ditto)

Steel

Axle Steel (Wohler)    ...
Axle Steel (Bauschinger)
Rail Steel (ditto)
^ ; Spring Steel (Wohler) ...
I Boiler Steel (Bauschinger)

i'33
1-67

P. jpj.    Average   Stresses.—The   following
figures are here given, all in tons and inches :

r83
1-91

2'00
2-14

1-53
additional

Material.
	Tensile Stress
		Extension per cent, at breaking.

	Breaking
	Safe
	
Manganese Steel (14% Mn)
	60
	IO
	44

Nickel Steel (3% Ni for plates)    . . .
	37
	7*
	20

Nickel Steel (3.35% Ni for forging)
	45
	8
	*7j

Silicon Bronze
	28
	5
	3°

Aluminium Bronze
	30
	5
	25

Delta Metal (forged)        ......
	30
	5
	

Delta Metal (cast) ...        ......
	20
	3*
	__

Sterro Metal         .........
	27
	4*
	—

(Seep. 1075.)